Generally, a ball joint is configured to rotatably connect a shaft member to an outer body and to absorb exterior impact applied to the shaft member. For example, the ball joint is used to a suspension system that prevents vibration or impact applied to an axle of a driving vehicle from a road from being directly transmitted to a vehicle body. Particularly, the ball joint is used to fix a stabilizer for preventing rolling of the vehicle or suspension link arms for maintaining angles of wheels of the vehicle.
If torsion or torque occurs at the shaft member such as the stabilizer or the suspension link arms due to external factors such as the rolling of the vehicle body or height changes of the wheels of the vehicle, a mounting apparatus such as the ball joint is configured to fix the shaft member to the outer body, that is the vehicle body.
Generally, the mounting apparatus includes a bushing for absorbing axial displacement and forward/rearward impact, and a bracket enclosing the bushing and coupled to the outer body. A rubber bushing provided with a rubber between a hollow inner pipe and a hollow outer pipe or a pillow ball joint including a spherical ball formed on a hollow shaft and a bearing enclosing the ball and being slidable on the ball is used as the bushing.
The rubber bushing is excellent in absorbing forward/rearward impact and restoring its original position, but has low rigidity because a gap in a radial direction is formed therein. On the contrary, the pillow ball joint has high rigidity because a gap in the radial direction is not formed, but is bad at restoring its original position.
Therefore, the pillow ball joints are not used at both sides of the shaft member, and the rubber bushing should be used at at least one side of the shaft member.
In addition, a lubricant is injected into the pillow ball joint so as to smoothen rotation of the bearing along the spherical ball. At this time, an additional sealing member is coupled to the pillow ball joint in order to prevent leakage of the lubricant to the outside. Therefore, manufacturing processes and production cost of the pillow ball joint may be increased.